For many years, it has been common practice to insulate the cavity defined between the inner tank of a water heater and its outer shell with various types of fibreglass and other batting materials. Fiberglass is difficult to handle and may be hazardous to one's health; therefore, there is a movement towards the use of foamed insulative materials for insulating water heaters. Aside from health reasons, more importantly, foamed insulative materials have a better heat insulating value than fibreglass, so that either thinner layers of insulation may be used to provide the same degree of insulation as with fiberglass, or much thicker foamed insulative materials may be used to increase the insulation value for the water heater.
Various types of waer heaters, as insulated with foamed insulation, are disclosed, for example, in U.S. Pat. No. 3,253,731 and Canadian Pat. No. 885,831. Various techniques have been employed to contain the foam when injected into the cavity between the inner tank and the outer surronding shell. Particularly, with gas-fired water heaters, it is most important to isolate the foamed insulative material from the hot regions of the gas burner area. This is particularly important when using foamed polyurethanes, because the isocyanate component of the polyurethane, when burned, releases toxic gases.
In the art of insulating with foam materials, various techniques have been developed. For example, in U.S. Pat. No. 3,313,020, a railcar is insulated with a foam material. To define cavities in the area to be insulated, tubes of polyethylene are filled with a foam material. The formed cavities are subsequently insulated with additional foam material. The polyethylene tubes, as filled with foam, remain in the cavity.
Similar approaches have been used in insulating water heaters, such as the unit sold by Rheem International of Montgomery, Ala. A polyethylene bag is provided about the base of the inner tank of a water heater. The bag is expanded with foam insulation to seal off the lower portion of the cavity. Post-foaming insulative material is then introduced into the upper region of the cavity to complete insulation of the water heater tank. The bag with foam remains with the water heater. Sometimes the bag is over expanded with foam, causing it to burst. The unset foam can flow below the inner tank and may result in an ineffective seal for the cavity.
U.S. Pat. No. 4,296,799 discloses an approach for insulating a solar water tank where an inflatable bag is located within the tank and polyurethane foam is injected between the inflated bag and the outer shell of the tank. When the foam sets, the bag is supported for defining the interior holding portion of the tank.
Another approach in containing the insulative foam material about the inner tank of a water heater is provided by State Industries of Ashland, Tenn. A bulky preformed bag surrounds the entire tank into which foam insulative material is injected. The bag contains the foam in the cavity between the inner tank and the outer shell. Difficulties arise in placing the bag about the tank and bursting the bag if too much foam is injected.
The method and apparatus, according to this invention, overcomes the above problems in providing a simple technique for insulating water heaters. The method readily provides access for inspection of the set foam to ensure that foam has not leaked beneath the inner tank, which could be exposed to the high temperatures of a gas or oil burner or electrical heater components.